Mail processing systems for printing postage indicia on envelopes and other forms of mail pieces have long been well known and have enjoyed considerable commercial success. There are many different types of mail processing systems, ranging from relatively small units that handle only one mail piece at a time, to large, multi-functional units that can process thousands of mail pieces per hour in a continuous stream operation. The larger mailing machines often include different modules that automate the processes of producing mail pieces, each of which performs a different task on the mail piece. The mail piece is conveyed downstream utilizing a transport mechanism, such as rollers or a belt, to each of the modules. Such modules could include, for example, a singulating module, i.e., separating a stack of mail pieces such that the mail pieces are conveyed one at a time along the transport path, a moistening/sealing module, i.e., wetting and closing the glued flap of an envelope, a weighing module, and a metering module, i.e., applying evidence of postage to the mail piece. The exact configuration of the mailing machine is, of course, particular to the needs of the user.
Typically, one or more control devices, such as, for example, a microprocessor, performs user interface and controller functions for the mailing machine. Specifically, the control device provides all user interfaces, executes control of the mailing machine and print operations, calculates postage for debit based upon rate tables, provides the conduit for the Postal Security Device (PSD) to transfer postage indicia to the printer, operates with peripherals for accounting, printing and weighing, and conducts communications with a data center for postage funds refill, software download, rates download, and market-oriented data capture. The control device, in conjunction with an embedded PSD, constitutes the system meter that satisfies U.S. information-based indicia postage meter requirements and other international postal regulations regarding closed system meters. The United States Postal Service (USPS) initiated the Information-Based Indicia Program (IBIP) to enhance the security of postage metering by supporting new methods of applying postage to mail. The USPS has published draft specifications for the IBIP. The requirements for a closed system are defined in the “Performance Criteria for Information-Based Indicia and Security Architecture for Closed IBI Postage Metering System (PCIBI-C), dated Jan. 12, 1999. Part of the security required for postage metering systems includes the debiting of funds equivalent to the postage amount associated with a generated indicium, from the registers maintained within the PSD, upon printing of the indicium. The debiting occurs when the print operation is initiated, without regard to whether or not the printing has actually been completed.
The PCIBI-C specification defines the requirements for the indicium to be applied to mail produced by closed systems. An example of such an indicium is illustrated in FIG. 1. The indicium 10 consists of a two-dimensional (2D) barcode 12 and certain human-readable information 14. Some of the data included in the barcode can include, for example, the PSD manufacturer identification, PSD model identification, PSD serial number, values for the ascending and descending registers of the PSD, postage amount, and date of mailing. In addition, a digital signature is required to be created by the PSD for each mail piece and placed in the digital signature field of the barcode. Verification of an indicium is performed by the postal service scanning a mail piece to read the 2D barcode and verifying the information contained therein, including the digital signature. If the verification is unsuccessful, indicating that the indicium may not be authentic, the mail piece may not be delivered.
Since postal services accept indicia printed by postage meters and mailing machines as conclusive proof of payment of the amount of postage indicated, such devices are in effect machines for printing money. As a result postal services have imposed high standards for the print quality of indicia images produced by such machines. Even if an indicium is valid, if the verification equipment is unable to read the indicium, verification will not be possible. To avoid the loss of funds, postal services will provide refunds for “spoiled” mail pieces, i.e., mail pieces for which verification will not be possible or will not be mailed because of damage. Spoiled mail pieces can include mail pieces on which an indicium was properly printed but have been damaged prior to induction by the postal service (such as, for example, by being torn or mutilated in an inserting machine, sorting machine or the like) as well as mail pieces for which an indicium was attempted to be printed, but because of a malfunction of the printing device, was improperly printed and therefore would not be readable by automated equipment. In either situation, there must be some evidence of printing of an authentic indicium, i.e., an indicium that was properly generated and accounted for within the registers of the PSD. Such evidence is typically provided by the obtaining at least a portion of the indicium, e.g., one or more portions of the human readable portion or machine readable portion, such as the PSD serial number, values for the ascending and descending registers of the PSD, postage amount, and date of mailing, and verifying it with the records maintained by the PSD to confirm that the PSD did in fact generate the indicium.
In recent years, ink jet printing systems have been utilized in mail processing systems. Ink jet printing systems, as used herein, includes any form of printing wherein print control signals control a print mechanism to eject ink drops to produce a matrix of pixels, i.e. picture elements, to represent an image. An ink supply, typically in the form of a reservoir, supplies ink to the print mechanism. A problem with ink jet printing systems, however, is that they are susceptible to different kinds of failures, some of which are complete failures that can occur with no prior warning. An example of such a failure occurs in ink jet print heads that are not provided with a mechanism to release accumulated air within the print head. Ink jet print heads heat the ink to expel it from the nozzles of the print head. As the ink is heated, air bubbles are formed that accumulate internally within the print head. These air bubbles displace the ink provided to the nozzles. Failure to vent these air bubbles will eventually result in sufficient air pressure such that the print head will be denied ink, even if the reservoir is full. As such, none of the ink jet nozzles will be able to print, resulting in a total failure of the print head. This type of failure is unpredictable, and can occur suddenly without any warning, such as a gradual degradation of images previously printed.
For high speed mailing machines capable of processing mail pieces at rates of 18,000 letters per hour (300 letters per minute), a compete failure can result in the loss of postage funds at a rate of one to two dollars per second until the failure is noticed by an operator. Since there is a complete failure of the print head, there is no evidence of any kind that printing was attempted. The postal service, therefore, will not accept any mail pieces for delivery on which indicia, although properly generated and paid for, have not been printed, nor will the postal service provide any refund for the indicia that have been properly generated and paid for, but never printed, because of such a complete print head failure.